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Why lie detection methods don’t work

On Behalf of | Feb 2, 2024 | Criminal Defense

Most people in Maryland are familiar with the concept of lie detector tests. They appear in many television shows and movies where suspects are asked to submit to a polygraph test to determine their innocence or guilt. However, in real life, these tests have many fundamental flaws. They aren’t as foolproof as we have been led to believe. Let’s take a look at a few problems they have.

Polygraphs aren’t always accurate

Lie detector tests usually rely on physiological changes in a person like an increased heart rate. However, these don’t always work as some people have no physical or emotional response while lying.

Criminal defense research currently suggests that these tests are roughly 70% accurate. When the legal requirement for a conviction is “beyond a reasonable doubt,” a 30% chance of an incorrect result makes the test effectively useless.

Body language analysis doesn’t work either

Another method commonly used as an alternative to a polygraph is a physical analysis of subtle behaviors. This involves a body language expert looking for micro-expressions or other “tells” that reveal when a person is lying. Similar to polygraphs or eyewitness testimony, criminal justice experts believe that there is a significant chance for inaccuracy.

Potential future alternatives

There are a few ideas that may work in the future, although they have not been successfully implemented at this time, including:

  • MRI/fMRI scans
  • AI detection
  • Criterion-based content analysis

Final thoughts

Lie detector tests have been used by law enforcement for years but research has shown that even the best current methods are only about 70% accurate. That may change in the future but with lives on the line, a 30% margin for error is too high.